A noise killer circuit (also referred to as “noise canceler”) has been known which eliminates a pulse-like noise signal component from a radio input audio signal by previous value hold or interpolation processing. However, the noise killer circuit can sometimes add rasping burst noise when operating too much.
To solve the problem, a noise elimination method has conventionally been proposed which detects the symmetry of an input data waveform based on a certain threshold, and controls, when detecting an asymmetric waveform, in such a manner as to prevent the output of the data (see Patent Document 1, for example).    Patent Document 1: Japanese Patent Laid-Open No. 59-165549.
However, according to the noise elimination method disclosed in the foregoing Patent Document 1, it can detect only a symmetric waveform synchronized with a reference sampling period, and cannot detect the symmetry unless the value during the sampling is constant. Thus, it is unsuitable for detecting a pulse-like waveform.
Accordingly, some possibility cannot be denied that the noise elimination circuit included in the radio receiving apparatus can generate a signal waveform slightly different from its original form for the pulse-like radio input audio signal waveform, and add as the rasping burst noise.
The present invention is implemented to solve the foregoing problem. Therefore it is an object of the present invention to provide a radio receiving apparatus and a noise elimination method in the same apparatus capable of achieving appropriate control of a noise elimination circuit that is likely to generate a signal waveform different from the original form and to add it as noise by limiting the operation of the noise elimination circuit depending on the radio input audio signal waveform.